Traces of at least two unknown people were discovered at the London apartment of a British spy whose naked body was found locked inside a sports bag, a forensic expert told a hearing Monday.

Ros Hammond said DNA from two as yet unidentified people had been found inside the home, and that tests still being conducted could provide a breakthrough in the case, which has so far baffled investigators.

Gareth Williams, 31, worked for Britain's secret eavesdropping service GCHQ but was attached to the MI6 overseas spy agency when his remains were found in August 2010 at his London apartment inside the bag, and placed in a bathtub.

A London inquest hearing has been told that Williams rarely invited guests into his government-provided apartment, but Hammond said scientists had uncovered possible evidence of visitors.

"There's certainly evidence of at least two people other than Mr. Williams on the samples tested," Hammond told Westminster Coroner's Court.

She said DNA evidence on a towel was still being examined and could provide a clue to explain Williams' puzzling death. "There's hope," she said. "The tests are still in progress and there may be some promising results."

Police say they are not certain exactly how Williams died and have so far made no arrests, although a senior detective has told the inquest she believes that at least one other person must have been involved.

Officers have suggested Williams' death may have had links to his private life and an apparent interest in sadomasochism _ possibly during a sexual encounter gone awry. His relatives, however, insist his demise must be related to his highly secret work.

Pathologists told the hearing that poisoning or asphyxiation may have killed Williams, but acknowledged they can't be certain of the exact cause of his death because his cadaver badly decomposed as it lay undiscovered for several days.

MI6 colleagues failed to report Williams as missing for a week, meaning that police and pathologists lost vital chances to gather evidence.

Pathologist Benjamin Swift told the inquest that radiators had been turned on inside Williams' apartment _ even though it was summer _ accelerating the decomposition of his body.

Asked whether Williams may have been poisoned or suffocated, Swift said the options "were certainly two of the more prominent" explanations for the cryptology expert's death.

"I would never say never but those are the foremost contenders," he told the hearing.

Pathologist Richard Shepherd, who carried out the third of three autopsies on Williams, said it appeared certain the spy climbed into the bag voluntarily.

It was more likely that Williams "was alive when he entered the bag than that he was dead," the told the hearing.

Shepherd said it would have been very difficult to place Williams' dead body inside the duffel bag in the position it was found in. He was discovered in the fetal position with his arms folded across his chest.

There were also no signs that the spy had struggled to free himself.

"Were he to be alive and struggling I would anticipate there to have been injuries," Shepherd said.

A verdict from the inquest is expected Wednesday.